Mistletoe Mishap
by Lady Azura
Summary: What happens when a pair of unsuspecting step-siblings get caught under the mistletoe? Secret Santa challenge.


Summary: _What happens when a pair of unsuspecting step-siblings get caught under the mistletoe? (Secret Santa challenge.)_

Disclaimer: Don't own _Life With Derek_. 'Nuff said.

Author's Note: Okay, so this is my Secret Santa gift to **Ally**.

Enjoy!

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**Mistletoe Mishap****  
**_**By: Lady Azura**_

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Good _God_.

What the hell was _wrong_ with him?

That's what Derek Venturi wanted to know after catching himself thinking about his step-sister for the umpteenth time that night, ever since he'd walked through the front door and saw her standing there, foolishly assuming her to be his brother's latest girlfriend only to be corrected in the most humiliating manner imaginable, which ultimately reminded him why he stopped visiting in the first place. Not because of _her_, specifically, but step-siblings -- step-_sisters_ -- in general… namely older ones. Namely _the_ older one, in this particular case.

Or at least, she _used_ to be the reason.

Now, it seemed, it was her sister. His _much younger_ step-sister. The one he was _supposed_ to see as an actual sister, like Marti. Hell, it was bad enough that he used to like Casey, but now _Lizzie_?

Fate truly had it out for him, it seemed.

Okay, so perhaps the age thing wasn't a major issue, but that still didn't change the fact that they were practically blood now, ever since the birth of Lex six years earlier. _Their_ younger brother; the link that bound the five (now six) siblings together. That was Alexander Evan McDonald-Venturi in a nutshell.

And yet, that knowledge failed to stop the fantasies that crept into his mind every time he laid eyes on Lizzie. In his defense, however, Lizzie wasn't the same Lizzie she'd been when the McDonalds had first moved in, or even when he and Casey had left for university. She'd grown up _a lot_. At eighteen, she was almost as tall as her sister, minus an inch and a half or so, and had filled out quite nicely. Her hair had grown longer, her waist more prominent and her _chest_…

Ahem.

In short, Casey had competition.

But at least she'd always have her legs, Derek mused. At least until she popped out a few kids and succumbed to stretch marks and cellulite.

Granted, Lizzie wasn't the _only_ one who'd changed in the past six (almost seven!) years. Everyone had. For instance, Marti had gotten bigger and taken a liking to dyeing her hair abnormal colors (pink, blue, purple, lime green… the list was never-ending); Edwin had grown taller and gotten a pair of thin-rimmed glasses that, for whatever reason, made him look cooler than he did before; Casey had somehow managed to summon the courage to actually _chop off_ her chestnut locks after deciding that she was "too old" for long hair, and that it didn't make her look sophisticated enough -- especially for an up-and-coming lawyer, such as herself; and finally, while their parents hadn't really _changed_ much, per say, they certainly appeared more stressed out thanks to Lex, who was allegedly "worse than Derek".

The latter didn't know whether to feel proud or threatened.

Regardless, despite all of the changes in his merged family, it was _Lizzie_ he noticed the most and that frustrated him to the point where he couldn't even sleep. He knew that the second he closed his eyes, not-so-innocent images would immediately flood into his head and invade his dreams. Images of him taking her against the wall, or on the table, or of her going down on him; images that would undoubtedly make him wake up painfully hard and drenched in a sheet of cold sweat.

Ugh.

He needed a glass of water.

_Stat_.

And with that in mind, Derek sat up and threw his legs over the edge of the living room sofa (his makeshift bed for the time being, since Edwin had moved into _his_ room after the elder of the two had moved out, to make room for Marti who's room soon became Lex's when he was old enough. Not that anyone but _him_ minded, of course; Edwin was thrilled to obtain his idol's former bedroom and Marti loved the privacy she had up in the attic), rising to his feet only to stretch and crack his knuckles. Once finished, he ventured into the kitchen.

After swallowing an Advil and downing an entire glass of water, Derek placed it in the sink and turned back around with the intention of returning to his couch.

… Only to stop dead in his tracks when he spotted Lizzie standing on the other side of the island counter.

"Hey." She greeted with a wave, "What's up?"

Derek leaned against the edge of the sink and folded his arms in an attempt to look cool.

"Not much. You?" He said.

The brunette merely shrugged. "Oh, you know… stuff." She paused momentarily to eye him suspiciously. "You know, you've been acting kind of weird since you got here. Anything on your mind?"

_'Yeah, but I don't think _you_ want to hear about it.'_ Derek wanted to say, but decided against it. Instead, he shook his head. "Nah. Everything's fine. Just dandy."

"Are you sure?" Lizzie persisted.

"Positive." Derek lied, desperately trying not to look at her cleavage -- which was difficult, because she was wearing a loose tank top (and no bra, he noticed as well) and every time she leaned forward, that was all he could see.

Cleavage, cleavage, cleavage… and more cleavage.

If she were _any_ other girl… he'd totally make a move on her and he knew it.

Unfortunately, she wasn't. She was his step-sister.

She was _Lizzie_.

"So… what are you doing up so late?"

_'Thinking about you. Why?'_ Derek thought, but pursed his lips together in an attempt to keep from speaking those words aloud.

"Headache." He forced out instead, "You?"

"Couldn't sleep. I think Edwin snuck a girl in… I swore I heard them having sex." Lizzie made a disgusted face.

Derek laughed. "Maybe he's watching porn?"

He couldn't for the life of him picture Edwin having sex. Mostly because he didn't know why anyone in there right mind _would_ have sex with the guy… willingly, at least.

"Or jacking off." Lizzie added with a smirk.

Also likely, but Derek couldn't see why that would keep her up. It couldn't take Edwin _that_ long to finish, could it?

_Why_ were they even _talking_ about this to begin with?

Good grief!

"Well, I'm gonna try to get back to sleep. Hopefully Ed's done with… whatever he was doing." Lizzie announced with a sigh, turning around.

"Yeah." Derek joined her at the kitchen entrance. "See you in the morning."

The McDonald girl beamed.

"Thanks. You to… oh, shit!" The grin on her face immediately disappeared.

Derek furrowed his brow.

"What's wrong?" He asked.

"Look up."

The former slacker did as he was told and glanced up, only to have his jaw drop seconds later.

_'Oh, you've gotta be shittin' me…'_

There, hanging above the two unsuspecting step-siblings, was mistletoe.

An awkward silence dawned on them, only to be broken by Lizzie's nervous cough.

"So, umm… do you want to just… you know… pretend that this never happened?" She asked, "I mean… it's not like anyone's awake to see or anything… I mean, I know it'd be breaking tradition and all, but -"

Before Lizzie could even finish her sentence, Derek silenced her with a kiss. After about a minute or so, he quickly pulled back, licking his lips as he did so, and stared down at his step-sister's startled face, pink with embarrassment.

"Sorry," he said, clearing his throat and averting his gaze. "But I'm not exactly one to break tradition… if you know what I mean."

That was his story and he was stickin' to it whether she liked it or not.

"Really? Is that all?" Lizzie inquired, regaining her composure.

Derek frowned.

"Yeah…" He said slowly, "Why else would -"

He was cut off by Lizzie throwing her arms around his neck and capturing his lips with her own in a bruising kiss that left his lungs screaming for oxygen. By the time they actually parted for air, and also to assess the situation, her legs were wrapped around his waist and his fingers was inching dangerously close to the apex of her thighs.

"Wow," she panted heavily, letting her feet hit the floor, "that was… wow."

"Yeah." Derek agreed, stepping away and watching as she fixed her hair and clothes, all the while running his tongue along his bottom lip, which stung due to the ferocity of their second kiss.

"So, uh… I'm just gonna… you know…" Lizzie made a few motions to the staircase.

Derek nodded and bid her goodnight, watching her ascend to the second floor hallway. He waited until she was gone from his sight before making his way back into the living room and plopping down on the couch, grinning from ear-to-ear as he did so.

"Wow."

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FIN

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**I hope you enjoyed, Ally! Merry Christmas!**

**Please ****REVIEW****!**

_**-Lady Azura-**_


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